1. Field of the Invention
The present invention relates in general to the formation of an integrated circuit including capacitors. In particular, the present invention relates to a method for forming capacitors having uniform thickness of insulators while forming a damascene structure.
2. Description of the Related Art
Capacitors are integrated in various integrated circuits. For example, capacitors can be used as decoupling capacitors to provide improved voltage regulation and noise immunity for power distribution. These capacitors also have wide applications in analog/logic, analog-to-digital, mixed signal, radio frequency circuits and so on.
A conventional method of manufacturing a semiconductor apparatus including a capacitor 20 that is formed of metal-insulator-metal layers is described with reference to FIGS. 1Axcx9c1D. As shown in FIG. 1A, an aluminum layer is deposited on an insulator 12 which contains interconnections and is formed on a silicon substrate having devices (not shown) thereon and therein. The aluminum layer is then patterned by masking and etching to form wires 14a and 14b. As shown in FIG. 1B, an insulator 16 with a tungsten plug 18 (hereafter are referred to W-plug) for connecting the aluminum wire 14a and to-be-formed capacitor is formed on the aluminum wires 14a and 14b and the insulator 12. As shown in FIG. 1C, a first conductive plate 21, an insulator 22 and a second conductive plate 23 are sequentially deposited on the insulator 16 and the W-plug 18, and then patterned by masking and etching to constitute a capacitor 20. The first conductive plate 21, which is used as the bottom electrode, is connected with the aluminum wire 14a through the W-plug 18. Another insulator 26 is deposited on the insulator 16 and the capacitor 20. The insulators 16 and 26 are patterned to form W-plug 28a and W-plug 28b. As shown in FIG. 1D, an aluminum layer (not shown) is deposited on the insulator 26 and the W-plugs 28a and 28b. The aluminum layer is then patterned by masking and etching to form wires 34a and 34b. The aluminum wire 34a is connected with the second conductive plate 23 through the W-plug 28a. The aluminum wire 34b is connected with the aluminum wire 14b through the W-plug 28b. 
The above-mentioned method for integrating the capacitor 20 into the integrated circuits is not cost-effective enough because it requires several masking steps to form the capacitor 20.
With the enhancements of the integration and the highly demanding speed of data transmission, the aluminum interconnections cannot satisfy these trends. Copper (Cu) has high electric conductivity to reduce RC delay and can be substituted for the aluminum as conducting wires. Using copper as the conducting wires need additional processes, that is, damascene processes. During the etching process using chlorine plasma, the boiling point of copper chloride (CuCl2) produced by copper and chlorine can reach temperature as high as 1500xc2x0 C., so copper cannot be patterned by conventional etching process.
A thin-film capacitor formed by combining with the Cu damascene processes is disclosed in U.S. Pat. No. 6,180,976 B1. In the ""976 B1 patent, the bottom electrode of the thin-film capacitor is also formed by the damascene process. The ""976 B1 patent has advantage of saving a masking step. However, a chemical mechanical polishing process is required to remove the undesirable metal material to form the bottom electrode. The dishing phenomenon is likely to occur on the bottom electrode and result in uneven surface. Therefore, the thickness of the insulator can not be controlled to be unvaried and uniform, thereby to stablize the electrical properies of the capacitors.
It is an object of the present invention to provide an improved method of forming a damascene structure having capacitors.
It is another object of the present invention to provide a method of forming a damascene structure having capacitors, which uses relatively fewer masking steps.
The present invention provides a method of forming a damascene structure having capacitors. Before fabricating the thin-film capacitor, a first Cu wire and a second Cu wire, surrouded with a barrier layer and a first sealing layer, are prepared in a first insulator. A second insulator and a stop layer are formed on the sealing layer in sequence. The first and second Cu plugs are disposed in the first sealing layer, the second insulator and the stop layer. A first metal layer, a fourth insulator and a second metal layer are formed on the stop layer in sequence. The second metal layer is subjected to photolithography and etching processes to become an upper electrode. Another photolithography and etching processes are then carried out to make the fourth insulator and the first metal layer to be pattened as a bottom electrode and a conducting wire. The bottom electrode is connected with the first Cu wire through the first Cu plug and the conducting wire is connected with the second Cu wire through the second Cu plug. A fifth insulator having a flat surface and dual damascene patterns therein is formed over the upper electrode, the fourth insulator and the stop layer. The third and fourth Cu wires with a second sealing layer thereon are formed in the trenches of the patterns and the third and fourth Cu plugs are formed in the holes of the patterns. The upper electrode is connected with the third Cu wire through the third Cu plug, and the conducting wire is connected with the fourth Cu wire through the fourth Cu plug.